The sensor system is here primarily used for the analysis of the travel path of the vehicle, for example in order to detect obstacles along the travel path, lane changes and properties of the road. The initial situation of the method is based on the steps of defining a specified speed by way of the driver and setting a safety speed that is reduced with respect to the specified speed by way of the cruise control unit, for example on the basis of a vehicle in front, and detecting lane change of the vehicle.
The field of application of the invention extends in particular to motor vehicles intended for long-distance traffic that comprise a cruise control unit for regulating the speed and a sensor system for perceiving the environment for the purposes of dynamic or adaptive adjustment of the speed regulation. The specified speed is here generally defined by the driver. A lane change is determined for example by optically capturing the lane using a camera and detecting the lane marking by targeted image analysis.
A typical situation when operating such a vehicle is that a radar is used to detect an obstacle vehicle in front and an adaptive cruise control unit is used to match the speed to the obstacle vehicle in front such that the vehicle drives with a safety speed that is reduced with respect to the predefined specified speed. If the obstacle vehicle in front then disappears as an obstacle, the adaptive cruise control unit once again sets the specified speed. The obstacle vehicle can disappear for example because it accelerates, turns off or because the following vehicle turns off, changes lane and/or overtakes the obstacle vehicle.
In particular, the following vehicle can change to a lane that leads to an off-ramp or exit ramp from the respective freeway or highway, that is to say for example an autobahn or two-way expressway. On such exit ramps, the speed of the vehicle must be lowered below the specified speed that is typical for the highway. For this reason, the adaptive cruise control unit may disadvantageously re-accelerate the vehicle initially for a short time here, because no obstacle is present anymore, while the vehicle shortly thereafter, at the latest in a bend of the exit ramp, must be braked again by a further driver assistance system or by the driver. This means first, that fuel or brakes are used or worn unnecessarily, and possibly also requires an additional intervention in the speed regulation that is unpleasant for the driver.
Patent document U.S. Pat. No. 7,260,465 B2 discusses a method for regulating the speed, in which a navigation system that comprises a positioning system such as GPS and map material is used to determine, by way of comparison to the position determined using GPS and on the basis of coordinates of off-ramps or exit ramps that are marked on the map, whether the vehicle is about to turn off onto such an exit ramp. If this is the case, and specifically before an adaptive cruise control unit had lowered the speed due to an obstacle, acceleration of the vehicle is prevented, even if the adaptive cruise control unit releases it again because the obstacle has disappeared due to a lane change so as to prevent unnecessary short-term acceleration.
Another disadvantage of this method is that it is based on stored map material, which may be incomplete or contain errors. In addition, the method relies on the use of GPS or other satellite positioning systems, which do not work, or work only to a limited extent, for example in tunnels.